By means of transfer matrix method,we calculated the optical properties of photonic crystal narrow band filters,which are made of two sets of photonic crystals with different photonic band gaps.A set of filters at 1 500 nm with a channel interval of 0.80 nm and 0.08 nm for dense wavelength division multiplexing(DWDM) has been also designed.The results of simulation indicates that the transmission properties of this kind of filter can hardly be influenced by the reflective indexes of both sides of it.It can grow at one end of the optical fiber,or be planted within the optical fiber,or be used in air directly,which makes the system more simple and portable.